Apparatus for operating a clutch in an automated mechanical transmission

ABSTRACT

An apparatus and method for controlling the engagement rate of a clutch in a partially or fully automated mechanical transmission is responsive to certain calculations derived from the rotational speeds of the input member and the output member of the clutch. The apparatus includes an electronic controller which initially sets a desired speed for the vehicle engine during the shifting process, determines a rate of engagement movement of a release bearing of the clutch, and actuates appropriate valves to initiate the gradual engagement of the clutch. In a first embodiment, the electronic controller compares the rotational speeds of the input and output shafts of the clutch in order to determine if the difference therebetween is less than a first constant value. If so, it can be inferred that the clutch is sufficiently close to full engagement as to warrant the interruption the gradual engagement process and immediately move the release bearing from its current position to the fully engaged position. To avoid a false inference of full engagement, the clutch input or output shaft speed signal is compared with the desired engine speed signal. When the magnitude of the difference between the clutch input shaft speed signal and the desired engine speed signal is less than a second constant value, then the inference that the clutch is sufficiently close to full engagement is confirmed. Thus, the release bearing can be immediately moved from its current position to the fully engaged position. In a second embodiment, an updated difference signal (calculated as the difference between an updated clutch input shaft speed signal and an updated clutch output shaft speed signal) is compared with a previous difference signal. An error signal is calculated as the difference between the updated difference signal and the previous difference signal. The electronic controller controls the movement of the release bearing such that the error signal closely follows a selected clutch engagement profile so as to consistently engage the clutch.

BACKGROUND OF THE INVENTION

This invention relates in general to vehicle transmissions and inparticular to a method and apparatus for automatically controlling theoperation of a clutch for use with an automated mechanical transmissionin a vehicle drive train assembly.

In virtually all land vehicles in use today, a transmission is providedin a drive train between a source of rotational power, such as aninternal combustion or diesel engine, and the driven axle and wheels ofthe vehicle. A typical transmission includes a case containing an inputshaft, an output shaft, and a plurality of meshing gears. Means areprovided for connecting selected ones of the meshing gears between theinput shaft and the output shaft to provide a desired speed reductiongear ratio therebetween. The meshing gears contained within thetransmission case are of varying size so as to provide a plurality ofsuch gear ratios. By appropriately shifting among these various gearratios, acceleration and deceleration of the vehicle can be accomplishedin a smooth and efficient manner.

To facilitate the operation of the transmission, it is well known toprovide a clutch between the vehicle engine and the transmission. Whenthe clutch is engaged, the transmission is driven by the vehicle engineto operate the vehicle at a selected gear ratio. To shift thetransmission from a first gear ratio to a second gear ratio, the clutchis initially disengaged such that power is not transmitted from thevehicle engine to the transmission. This allows the gear shiftingoperation to occur within the transmission under a non-torque loadingcondition to prevent undesirable clashing of the meshing gear teeth.Thereafter, the clutch is re-engaged such that power is transmitted fromthe vehicle engine to the transmission to operate the vehicle at thesecond gear ratio.

A typical structure for a vehicle clutch includes a cover which isconnected to a flywheel secured to the end of the output shaft of thevehicle engine for rotation therewith. A pressure plate is disposedwithin the clutch between the cover and the flywheel. The pressure plateis connected for rotation with the flywheel and the cover, but ispermitted to move axially relative thereto. Thus, the flywheel, thecover, and the pressure plate are all constantly rotatably driven by thevehicle engine. Between the flywheel and the pressure plate, a drivendisc assembly is disposed. The driven disc assembly is supported on theinput shaft of the transmission for rotation therewith, but is permittedto move axially relative thereto. To engage the clutch, the pressureplate is moved axially toward the flywheel to an engaged position,wherein the driven disc assembly is frictionally engaged between theflywheel and the pressure plate. As a result, the driven disc assembly(and the input shaft of the transmission upon which it is supported) aredriven to rotate with the flywheel, the cover, and the pressure plate.To disengage the clutch, the pressure plate is moved axially away fromthe flywheel to a disengaged position. When the pressure plate is movedaxially to this disengaged position, the driven disc assembly is notfrictionally engaged between the flywheel and the pressure plate. As aresult, the driven disc assembly (and the input shaft of thetransmission upon which it is supported) are not driven to rotate withthe flywheel, the cover, and the pressure plate.

To effect such axial movement of the pressure plate between the engagedand disengaged positions, most vehicle clutches are provided with arelease assembly including a generally hollow cylindrical release sleevewhich is disposed about the output shaft of the clutch. The forward endof the release sleeve extends within the clutch and is connected througha plurality of levers or other mechanical mechanism to the pressureplate. In this manner, axial movement of the release sleeve causescorresponding axial movement of the pressure plate between the engagedand disengaged positions. Usually, one or more engagement springs areprovided within the clutch to urge the pressure plate toward the engagedposition. The engagement springs typically react between the releasesleeve and the cover to normally maintain the clutch in the engagedcondition. The rearward end of the release sleeve extends outwardly fromthe clutch through a central opening formed through the cover. Becausethe release sleeve is connected to the cover and the pressure plate ofthe clutch, it is also constantly driven to rotate whenever the vehicleengine is operating. Thus, an annular release bearing is usually mountedon the rearward end of the release sleeve. The release bearing isaxially fixed on the release sleeve and includes an inner race whichrotates with release sleeve, an outer race which is restrained fromrotation, and a plurality of bearings disposed between the inner raceand the outer race to accommodate such relative rotation. Thenon-rotating outer race of the release bearing is typically engaged byan actuating mechanism for moving the release sleeve (and, therefore,the pressure plate) between the engaged and disengaged positions tooperate the clutch.

In a conventional mechanical transmission, both the operation of theclutch and the gear shifting operation in the transmission are performedmanually by an operator of the vehicle. For example, the clutch can bedisengaged by depressing a clutch pedal located in the drivercompartment of the vehicle. The clutch pedal is connected through amechanical linkage to the outer race of the release bearing of theclutch such that when the clutch pedal is depressed, the pressure plateof the clutch is moved from the engaged position to the disengagedposition. When the clutch pedal is released, the engagement springsprovided within the clutch return the pressure plate from the disengagedposition to the engaged position. Similarly, the gear shifting operationin the transmission can be performed when the clutch is disengaged bymanually moving a shift lever which extends from the transmission intothe driver compartment of the vehicle. Manually operatedclutch/transmission assemblies of this general type are well known inthe art and are relatively simple, inexpensive, and lightweight instructure and operation. Because of this, the majority of medium andheavy duty truck clutch/transmission assemblies in common use today aremanually operated.

More recently, however, in order to improve the convenience of use ofmanually operated clutch/transmission assemblies, various structureshave been proposed for partially or fully automating the shifting of anotherwise manually operated transmission. In a partially or fullyautomated manual transmission, the driver-manipulated clutch pedal maybe replaced by an automatic clutch actuator, such as a hydraulic orpneumatic actuator. The operation of the automatic clutch actuator canbe controlled by an electronic controller or other control mechanism toselectively engage and disengage the clutch without manual effort by thedriver. Similarly, the driver-manipulated shift lever may also bereplaced by an automatic transmission actuator, such as a hydraulic orpneumatic actuator which is controlled by an electronic controller orother control mechanism to select and engage desired gear ratios foruse.

In both manually operated transmissions and in partially or fullyautomated manual transmissions, one of the most difficult operations toperform is to initially launch the vehicle from at or near astand-still. This is because the force required to overcome the inertiaof the vehicle is the greatest when attempting to initially acceleratethe vehicle from at or near zero velocity. This relatively large amountof inertial force results in a relatively large load being placed on thevehicle engine when the clutch is engaged during a vehicle launch. Thus,the movement of the release bearing from the disengaged position to theengaged position must be carefully controlled during the initial launchof the vehicle to prevent the engine from stalling and to avoidundesirable sudden jerking movement of the vehicle. Although the sameconsiderations are generally applicable when re-engaging the clutchduring subsequent shifting operations in the higher gear ratios of thetransmissions, the control of the movement of the release bearing fromthe disengaged position to the engaged position has been found to beless critical when shifting among such higher gear ratios because a muchlesser force is required to overcome the inertia of the vehicle when thevehicle is already moving.

To address these considerations, the total movement of the releasebearing from the disengaged position to the engaged position can bedivided into three ranges of movement. The first range of movement isfrom the disengaged position to a first intermediate position (referredto as the transition point). The transition point is selected to berelatively near, but spaced apart from, the position of the releasebearing at which the driven disc assembly of the clutch is initiallyengaged by the flywheel and the pressure plate. Thus, during this firstrange of movement (referred to as the transition movement), the clutchis completely disengaged, and no torque is transmitted through theclutch to the transmission. The second range of movement is from thetransition point to a second intermediate position (referred to as thekiss point). The kiss point is the position of the release bearing atwhich the driven disc assembly is initially engaged by the flywheel andthe pressure plate. Thus, during this second range of movement (referredto as the approach movement) from the transition point to the kisspoint, the clutch is disengaged until the release bearing reaches thekiss point, at which point the first measurable amount of torque istransmitted through the clutch to the transmission. The third range ofmovement of the release bearing is from the kiss point to the engagedposition. The engaged position is the position of the release bearing atwhich the driven disc assembly is completely engaged by the flywheel andthe pressure plate. Thus, during this third range of movement (referredto as the engagement movement), the clutch is gradually engaged so as toincrease the amount of torque which is transmitted through the clutch tothe transmission from the first measurable amount at the kiss point tothe full capacity of the clutch at the engaged position.

As mentioned above, during the engagement movement of the releasebearing from the kiss point to the engaged position, the clutch isgradually engaged so as to increase the amount of torque which istransmitted through the clutch to the transmission from the firstmeasurable amount at the kiss point to the full capacity of the clutchat the engaged position. Thus, although it is desirable that thisengagement movement of the release bearing be accomplished as quickly aspossible, it is still important to engage the clutch smoothly to preventthe engine from stalling and to avoid undesirable sudden jerkingmovement of the vehicle. In the past, the rate of engagement movement ofthe release bearing (referred to as the engagement rate) has beendetermined as a function of the difference between the rotational speedsof the input member and the output member of the clutch. However, it hasbeen found that such a comparison of input and output member rotationalspeeds may not be well suited for all of the varying conditions underwhich the vehicle may be operated. Thus, it would be desirable toprovide an apparatus and method for controlling the engagement rate of aclutch in a partially or fully automated mechanical transmission whichis better suited for all of the varying conditions under which thevehicle may be operated.

SUMMARY OF THE INVENTION

This invention relates to an apparatus and method for controlling theengagement rate of a clutch in a partially or fully automated mechanicaltransmission in response to certain calculations derived from therotational speeds of the input member and the output member of theclutch. The apparatus includes an electronic controller which initiallysets a desired speed for the vehicle engine during the shifting process,determines a rate of engagement movement of a release bearing of theclutch, and actuates appropriate valves to initiate the gradualengagement of the clutch. In a first embodiment, the electroniccontroller compares the rotational speeds of the input and output shaftsof the clutch in order to determine if the difference therebetween isless than a first constant value. If so, it can be inferred that theclutch is sufficiently close to full engagement as to warrant theinterruption the gradual engagement process and immediately move therelease bearing from its current position to the fully engaged position.To avoid a false inference of full engagement, however, the clutch input(or output) shaft speed signal is compared with the desired engine speedsignal. When the magnitude of the difference between the clutch inputshaft speed signal and the desired engine speed signal is less than asecond constant value, then the inference that the clutch issufficiently close to full engagement is confirmed. Thus, the releasebearing can be immediately moved from its current position to the fullyengaged position. In a second embodiment, an updated difference signal(calculated as the difference between an updated clutch input shaftspeed signal and an updated clutch output shaft speed signal) iscompared with a previous difference signal. An error signal iscalculated as the difference between the updated difference signal andthe previous difference signal. The electronic controller controls themovement of the release bearing of the clutch such that the error signalclosely follows a selected clutch engagement profile so as toconsistently engage the clutch.

Various objects and advantages of this invention will become apparent tothose skilled in the art from the following detailed description of thepreferred embodiments, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a vehicle drive train assembly including anelectronic controller in accordance with this invention.

FIG. 2 is sectional elevational view of the clutch actuator and portionsof the clutch and transmission illustrated in FIG. 1 showing the clutchactuator and the clutch in a disengaged position, together with a blockdiagram of the valves and related control circuitry for operating theclutch actuator and the clutch.

FIG. 3 is a flow chart of a first embodiment of an algorithm forcontrolling the movement of the release bearing of the clutch in itsengagement movement from the kiss point to the engaged position.

FIG. 4 is a flow chart of a second embodiment of an algorithm forcontrolling the movement of the release bearing of the clutch in itsengagement movement from the kiss point to the engaged position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, there is illustrated in FIG. 1 a blockdiagram of a vehicle drive train assembly, indicated generally at 10.The drive train assembly 10 includes a conventional engine 11 or othersource of rotational power. The engine 11 is connected through an outputshaft 11 a, such as a crankshaft of the engine 11, to a clutch 12. Theclutch 12 is also conventional in the art and functions to selectivelyconnect the output shaft 11 a of the engine 11 to an input shaft 13 a ofa transmission 13. The transmission 13 contains a plurality of meshinggears (not shown) which are selectively connected between the inputshaft 13 a and an output shaft 13 b. The meshing gears contained withinthe transmission 13 are of varying size so as to provide a plurality ofsuch gear ratios. By appropriately shifting among these various gearratios, a desired speed reduction gear ratio can be provided between theinput shaft 13 a and the output shaft 13 b. Consequently, accelerationand deceleration of the vehicle can be accomplished in a smooth andefficient manner. The output shaft 13 b is connected to a conventionalaxle assembly 14. The axle assembly 14 includes one or more wheels whichare rotatably driven by the engine 11 whenever the clutch 12 and thetransmission 13 are engaged. This general structure for the drive trainassembly 10 is well known in the art.

The illustrated transmission 13 may be either a partially or fullyautomated mechanical transmission. In a typical partially automatedmanual transmission, a driver-manipulated shift lever (not shown)engages and moves certain ones of a plurality of shift rails containedwithin the transmission to engage a first set of gear ratios for use.However, an automatically shifting transmission actuator 15 is providedon the transmission 13 to engage and move the remaining shift rails toengage a second set of gear ratios for use. For example, it is known toprovide a partially automated manual transmission wherein the lower gearratios are manually selected and engaged by the vehicle driver using theshift lever, while the higher gear ratios are automatically selected andengaged by the transmission actuator 15. One example of a typicalpartially automated manual transmission of this general structure isdisclosed in detail in U.S. Pat. No. 5,450,767, owned by the assigned ofthis application. The disclosure of that patent is incorporated hereinby reference. In a fully automated manual transmission, thedriver-operated shift lever is usually replaced by the transmissionactuator 15. The transmission actuator 15 functions to shift all of theshift rails contained within the transmission so as to select and engageall of the available gear ratios. The above-referenced patent discussesthe adaptability of the disclosed partially automated transmissionactuator 15 to fully automate the shifting of the transmission disclosedtherein.

To facilitate the automatic shifting of the transmission 15, the clutch12 is provided with a clutch actuator 16. The structure and operation ofthe clutch actuator 16 will be discussed further below. Briefly,however, the clutch actuator 16 is provided to replace adriver-manipulated clutch pedal so as to partially or fully automate theoperation of the clutch 12. The clutch actuator 16 is effective tooperate the clutch 12 in either an engaged or disengaged mode. When theclutch 12 is engaged, the transmission 13 is driven by the vehicleengine 11 to operate the vehicle at a selected gear ratio. To shift thetransmission 13 from a first gear ratio to a second gear ratio, theclutch 12 is initially disengaged such that power is not transmittedfrom the vehicle engine 11 to the transmission 13. This allows thetransmission actuator 15 to effect a gear shifting operation within thetransmission 13 under a non-torque loading condition to preventundesirable clashing of the meshing gear teeth. Thereafter, the clutch12 is re-engaged such that power is transmitted from the vehicle engine11 to the transmission 13 to operate the vehicle at the second gearratio.

The operation of the clutch actuator 16 and the transmission actuator 15are controlled by an electronic controller 20. The electronic controller20 can be embodied as any conventional microprocessor or similarcomputing apparatus which can be programmed to operate the clutchactuator 16 (to effect automatic disengagement and engagement of theclutch 12) and the transmission actuator 15 (to effect automaticshifting of the transmission 13 when the clutch 12 is disengaged) asdescribed above. The operation of the electronic controller 20 will bedescribed in detail below. A transmission output shaft speed sensor 21provides an input signal to the electronic controller 20. Thetransmission output shaft speed sensor 21 is conventional in the art andis adapted to generate an electrical signal which is representative ofthe actual rotational speed of the output shaft 13 b of the transmission13. A clutch position sensor 22 also provides an input signal to theelectronic controller 20. The structure and operation of the clutchposition sensor 22 will be described below.

An engine controller 23 is provided to control the operation of thevehicle engine 11. The engine controller 23 can also be embodied as anyconventional microprocessor or similar computing apparatus which can beprogrammed to operate the engine 11 in a desired manner. Primarily, theengine controller 23 controls the operation of the engine 11 in responseto an input signal generated by an accelerator pedal position sensor 24.The accelerator pedal position sensor 24 is conventional in the art andis adapted to generate an electrical signal which is representative ofthe actual position of the accelerator pedal (not shown) of the vehicle.As is well known, the accelerator pedal is physically manipulated by thefoot of the driver of the vehicle to control the operation thereof. Theaccelerator pedal is depressed by the driver when it is desired toincrease the speed of the engine 11 and move the vehicle. Conversely,the accelerator pedal is released when it is desired to decrease thespeed of the engine 11 to slow or stop such movement of the vehicle.Thus, the engine controller 23 controls the speed of the engine 11 inresponse to the signal from the accelerator pedal position sensor 24 soas to operate the vehicle as desired by the driver. The acceleratorpedal position sensor 24 may, if desired, be replaced by a throttleposition sensor (not shown) or other driver-responsive sensor whichgenerates a signal which is representative of the desired speed or modeof operation of the vehicle. A second input to the engine controller 23is an engine output shaft speed sensor 25. The engine output shaft speedsensor 25 is conventional in the art and is adapted to generate anelectrical signal which is representative of the actual rotational speedof the output shaft 11 a of the engine 11.

The electronic controller 20 and the engine controller 23 communicatewith one another over a data bus line 26 extending therebetween. In amanner which is generally conventional in the art, the electroniccontroller 20 and the engine controller 23 are programmed to communicateand cooperate with one another to so as to control the operation of thevehicle in a manner desired by the driver of the vehicle. Specifically,the electronic controller 20 and the engine controller 23 are effectiveto control the operation of the engine 11, the clutch 12, and thetransmission 13 in such a manner that the vehicle can be started andstopped solely by physical manipulation of the accelerator and brakepedals, similar to a conventional automatic transmission in a passengercar. To accomplish this, the signals from the accelerator pedal positionsensor 24 and the engine output shaft speed sensor 25 are available tothe electronic controller 20 over the data bus line 26. Alternatively,the signals from the accelerator pedal position sensor 24 and the engineoutput shaft speed sensor 25 can be fed directly to the electroniccontroller 20.

Referring now to FIG. 2, the clutch actuator 16 and portions of theclutch 12 and the transmission 13 are illustrated in detail. Thestructure and operation of the clutch actuator 16 are disclosed andillustrated in detail in co-pending application Ser. No. 08/775,460,filed Dec. 30, 1996 (owned by the assigned of this invention), thedisclosure of which is incorporated herein by reference. Briefly,however, the clutch actuator 16 includes an outer cylinder housing 30, ahollow cylindrical piston 31, and an inner cylinder housing 32. Thepiston 31 has at least one, and preferably a plurality, of axiallyforwardly projecting protrusions 31 a, each of which has acircumferentially extending groove 31 b formed therein. To assemble theclutch actuator 16, the piston 31 is initially disposed concentricallywithin the outer cylinder housing 30, and the inner cylinder housing 32is disposed concentrically within the piston 31. Then, the outercylinder housing 30 is secured to a forwardly facing surface of a caseof the transmission 13 by threaded fasteners (not illustrated) or othermeans. When this is done, a forwardly facing surface 32 a of the innercylinder housing 32 abuts a complementary shaped, rearwardly facingannular surface 30 a formed within the outer cylinder housing 30. At thesame time, a rearwardly facing surface 30 b of the outer cylinderhousing 30 abuts portions of the case of the transmission 13. Thus, theinner cylinder housing 32 is captured between the case of thetransmission 13 and the outer cylinder housing 30 so as to be fixed inposition relative thereto. At the same time, a circumferential rimportion 31 c of the piston 31 is received in an undercut 30 c formed inthe interior of the outer cylinder housing 30. Thus, the piston 31 iscapable of limited axial movement relative to the outer cylinder housing30 and the inner cylinder housing 32.

The clutch 12 is a conventional pull-to-release type clutch and includesa cover 12 a which is connected to a flywheel (not illustrated) which,in turn, is connected to the output shaft 11 a of the engine 11. Theflywheel and the cover 12 a are thus rotatably driven by the engine 11of the vehicle for rotation about an axis. The cover 12 a has a centralopening formed therethrough which receives a hollow, generallycylindrical release sleeve 12 b. The release sleeve 12 b is disposedconcentrically about the transmission input shaft 13 a. A driven discassembly (not shown) is mounted within the clutch 12 on the forward endof the transmission input shaft 13 a for rotation therewith and foraxial movement relative thereto. When the clutch 12 is engaged, torqueis transmitted from the driven disc assembly to the transmission inputshaft 13 a in a known manner. When the clutch 12 is disengaged, notorque is transmitted from the driven disc assembly to the transmissioninput shaft 13 a.

A forward end of the release sleeve 12 b has an annular groove formedthereabout which receives the radially innermost ends of a plurality ofclutch operating levers 12 c therein. Thus, axial movement of therelease sleeve 12 b causes pivoting movement of the clutch operatinglevers 12 c which, in turn, causes engagement and disengagement of theclutch 12 in a known manner. A plurality of clutch engagement springs 12d (only one of which is illustrated) reacts between the cover 12 a andthe forward end of the release sleeve 12 b. The ends of the clutchengagement springs 12 d are preferably supported on respective seatsprovided on the release sleeve 12 b and the cover 12 a. The springs 12 durge the release sleeve 12 b axially forwardly (toward the left whenviewing FIG. 2) toward an engaged position, wherein the components ofthe clutch 12 are frictionally engaged so as to cause the transmissioninput shaft 13 a to be rotatably driven by the engine 11. When therelease sleeve 12 b is moved axially rearwardly (toward the right whenviewing FIG. 2) against the urging of the engagement springs 12 d towarda disengaged position, the components of the clutch 12 are frictionallydisengaged so as to prevent the transmission input shaft 13 a from beingrotatably driven by the engine 11.

The rearward end of the release sleeve 12 b extends axially rearwardlythrough the central opening in the cover 12 a. An annular releasebearing 33 is disposed about the rearward end of the release sleeve 12 band is retained on one side by a snap ring 34 disposed within an annulargroove. A retaining ring 35 is also disposed about the rearward end ofthe release sleeve 12 b adjacent to the forward side of the releasebearing 33. A snap ring 36 is disposed in an annular groove in therelease sleeve 12 b to retain the retaining ring 35 on the releasesleeve 12 b. Thus, the release bearing 33 and the retaining ring 35 aresecured to the release sleeve 12 b for axial movement therewith. A snapring 37 is disposed within the groove formed in the outer surface of theretaining ring 35. The snap ring 37 connects the piston 31 with theretaining ring 35 such that axial movement of the piston 31 causescorresponding axial movement of the retaining ring 35, the releasebearing 33, and the release sleeve 12 b.

An annular chamber 38 is defined between the outer surface of the bodyof the piston 31, the enlarged rim portion 3 1 c formed at the rearwardend of the piston 31, and the undercut 30 c formed in the inner surfaceof the outer cylinder housing 30. The chamber 38 is sealed to form afluid-tight chamber by sealing elements, such as O-rings. A radiallyextending port 39 is formed through the outer cylinder housing 30. Aswill be explained in detail below, pressurized fluid (hydraulic orpneumatic, as desired) is supplied through the port 39 used to effectaxial movement of the piston 31 in one direction relative to the outercylinder housing 30 and the inner cylinder housing 31.

The clutch position sensor 22 is mounted on the outer cylinder housing30 for generating an electrical signal which is representative of theaxial position of the piston 31 relative to the outer and inner cylinderhousings 30 and 32. Such an electrical position signal is used by anelectronic controller 20 for automatically operating the clutch actuator16 in a manner described in detail below. The clutch position sensor 22is conventional in the art.

The port 39 communicates through a conduit 40 with an engage valve 41and a disengage valve 42. The engage valve 41 communicates with areservoir (in hydraulic systems) or the atmosphere (in pneumaticsystems), while the disengage valve 42 communicates with a source ofpressurized fluid 43, either hydraulic or pneumatic as desired. Theoperation of the engage valve 41 is controlled by an engage solenoid 44,while the operation of the disengage valve 42 is controlled by adisengage solenoid 45. The engage solenoid 44 and the disengage solenoid45 are, in turn, connected to the electronic controller 20 so as to beselectively operated thereby.

The clutch 12 is normally maintained in the engaged position under theinfluence of the engagement springs 12 d. When it is desired todisengage the clutch 12, the engage solenoid 44 is actuated by theelectronic controller 20 to close the engage valve 41, and the disengagesolenoid 45 is actuated by the electronic controller 20 to open thedisengage valve 42. As a result, pressurized fluid from the source 43 issupplied to the chamber 38, causing the piston 31 to move rearwardly(toward the right when viewing FIG. 2) against the urging of theengagement springs 12 d. As discussed above, such rearward movement ofthe piston 31 causes the clutch 12 to be disengaged. For several reasonswhich are well known in the art, the disengage valve 42 is operated bythe electronic controller 20 in an on-off manner, i.e., either wide openor completely closed.

When it is desired to subsequently re-engage the clutch 12, the engagesolenoid 44 is actuated by the electronic controller 20 to open theengage valve 41, and the disengage solenoid 45 is actuated by theelectronic controller 20 to close the disengage valve 42. As a result,the chamber 38 is vented to the reservoir, causing the piston 31 to moveforwardly (toward the left when viewing FIG. 2) under the influence ofthe engagement springs 12 d. As discussed above, such forward movementof the piston 31 causes the clutch 12 to be engaged. For several reasonswhich are well known in the art, the engage valve 44 is operated usingpulse width modulation techniques to control the engagement of theclutch 12. The electronic controller 20 varies the duty cycle of thepulse width modulation of the engage valve 41 so as to adjust the rateat which the pressurized fluid in the chamber 38 is vented to thereservoir. By adjusting the rate of venting of the chamber 38 in thismanner, the speed at which the release bearing 33 is moved from thedisengaged position to the engaged position can be precisely controlled.Precise control of the speed of movement of the release bearing from thedisengaged position to the engaged position is important to engage theclutch 12 smoothly and avoid undesirable sudden jerking movement of thevehicle.

As discussed above, the total movement of the release bearing 33 fromthe disengaged position to the engaged position can be divided intothree ranges of movement. The first range of movement of the releasebearing 33 is from the disengaged position to a first intermediateposition (referred to as the transition point). The transition point isselected to be relatively near, but spaced apart from, the position ofthe release bearing 33 at which the driven disc assembly of the clutch12 is initially engaged by the flywheel and the pressure plate. Thus,during this first range of movement (referred to as the transitionmovement), the clutch 12 is completely disengaged, and no torque istransmitted through the clutch 12 to the transmission 13. The secondrange of movement of the release bearing 33 is from the transition pointto a second intermediate position (referred to as the kiss point). Thekiss point is the position of the release bearing 33 at which the drivendisc assembly is initially engaged by the flywheel and the pressureplate. Thus, during this second range of movement (referred to as theapproach movement) from the transition point to the kiss point, theclutch 12 is disengaged until the release bearing 33 reaches the kisspoint, at which point the first measurable amount of torque istransmitted through the clutch 12 to the transmission 13. The thirdrange of movement of the release bearing 33 is from the kiss point tothe engaged position. The engaged position is the position of therelease bearing 33 at which the driven disc assembly is completelyengaged by the flywheel and the pressure plate. Thus, during this thirdrange of movement (referred to as the engagement movement), the clutch12 is gradually engaged so as to increase the amount of torque which istransmitted through the clutch 12 to the transmission 13 from the firstmeasurable amount at the kiss point to the full capacity of the clutch12 at the engaged position.

Movement of the release bearing 33 through the first and second rangesof movement can be accomplished in any known manner. As suggested above,the initial movement of the release bearing 33 from the disengagedposition to the transition point can be accomplished by pulse widthmodulating the engage valve 41 at a predetermined duty cycle so as tocause rapid movement of the release bearing 33 from the disengagedposition to the transition point. To accomplish this, the engage valve41 may be pulse width modulated at a constant rate throughout thetransition movement of the release bearing 33. Alternatively, the engagevalve 41 may be pulse width modulated at a rate which varies with thecurrent position of the release bearing 33 relative to the transitionpoint so as to decelerate the release bearing 33 somewhat as itapproaches the transition point. The electronic controller 20 can beprogrammed to monitor the clutch position signal from the clutchposition sensor 22 to determine when the release bearing 33 has reachedthe transition point. Regardless of the specific transition rate whichis used, it is desirable that the initial transition movement of therelease bearing 33 be performed as rapidly as possible because theclutch 12 is completely disengaged throughout. Therefore, no sudden andundesirable engagement of the clutch 12 will occur during this initialtransition movement of the release bearing 33.

Similarly, the approach movement of the release bearing 33 from thetransition point to the kiss point can be accomplished by pulse widthmodulation of the engage valve 41 at a duty cycle which is initiallyrelatively long (to initially maintain the rapid movement of the releasebearing 33), but subsequently is shortened to decelerate the releasebearing 33 as it approaches the kiss point. By slowing the movement ofthe release bearing 33 as it approaches the kiss point, the clutch 12will be engaged smoothly so as to prevent the engine from stalling andavoid undesirable sudden jerking movement of the vehicle. The electroniccontroller 20 can be programmed to automatically alter the duty cycle ofthe engage valve during this approach movement of the release bearing 33in response to sensed operating conditions. For example, the electroniccontroller 20 can be responsive to the amount of depression of theaccelerator pedal from the pedal position sensor 24 for adjusting theduty cycle of the engage valve. However, any known algorithms may beused to control the movement of the release bearing 33 in its initialtransition movement from the disengaged position to the transitionpoint, and in its subsequent approach movement from the transition pointto the kiss point.

The algorithm of this invention relates to the control of the movementof the release bearing 33 in its engagement movement from the kiss pointto the engaged position. As discussed above, during the engagementmovement of the release bearing 33 from the kiss point to the engagedposition, the clutch 12 is gradually engaged so as to increase theamount of torque which is transmitted through the clutch 12 to thetransmission 13 from the first measurable amount at the kiss point tothe full capacity of the clutch 12 at the engaged position. Thus,although it is desirable that this engagement movement of the releasebearing 33 be accomplished as quickly as possible, it is still importantto engage the clutch 12 smoothly to prevent the engine from stalling andavoid undesirable sudden jerking movement of the vehicle.

Referring now to FIG. 3, there is illustrated a flow chart of a firstembodiment of an algorithm, indicated generally at 50, for controllingthe movement of the release bearing 33 in its engagement movement fromthe kiss point to the engaged position. In the first step 51 of thealgorithm 50, the electronic controller 20 issues a command to theengine controller 23 setting a desired engine speed signal V_(ENG). Thedesired engine speed signal V_(ENG) is selected to be sufficiently highsuch that the engine 11 is capable of overcoming the inertia of thevehicle as the clutch 12 is engaged and thereby avoid stalling duringthe engagement process. The desired engine speed signal V_(ENG) can,therefore, vary with the specific structure of the engine 11, thetransmission 13 used in conjunction with the engine 11, and otherfactors. The second step 52 of the algorithm 50 is to determine theengagement rate of the release bearing 33 of the clutch 12. For thepurposes of this invention, the engagement rate can be determined in anyconventional manner in response to a number of operating conditions ofthe vehicle. For example, the engagement rate can be selected to be aconstant rate or may vary with the movement of the release bearing 33from the kiss point to the engaged position in the manner discussedabove. As will become apparent below, the algorithm 50 of this inventionmonitors the status of clutch engagement and alters the predeterminedengagement rate under certain circumstances. Then, as shown in the thirdstep 53 of the algorithm 50, the engage valve 41 and the disengage valve42 are actuated (by means of the respective solenoids 44 and 45) toeffect movement of the release bearing 33 of the clutch 12 according tothe selected engagement rate. Thus, the clutch engagement process isinitiated.

Next, the fourth step 54 of the algorithm 50 causes the electroniccontroller 20 to read the clutch input shaft speed signal V_(IN) fromthe engine controller 23. As discussed above, the engine output shaftspeed sensor 25 generates the clutch input shaft speed signal V_(IN) tothe engine controller 23 which is representative of the actualrotational speed of the output shaft 11 a of the engine 11. Thatinformation is available to the electronic controller 20 from the enginecontroller 23 over the data bus line 26. In the fifth step 55 of thealgorithm 50, the electronic controller 20 reads the transmission outputshaft speed signal directly from the speed sensor 21. The sixth step 56in the algorithm 50 is to calculate the clutch output shaft speed signalV_(OUT). The clutch output shaft speed signal V_(OUT) can be calculatedby multiplying the transmission output shaft speed with the gear ratioof the transmission 13 selected by the electronic controller 20 andimplemented by the transmission actuator 15.

The algorithm 50 next enters a decision point 57, wherein the clutchinput shaft speed signal V_(IN) is compared with the clutch output shaftspeed signal V_(OUT). In this step, the magnitude of the differencebetween the clutch input shaft speed signal V_(IN) and the clutch outputshaft speed signal V_(OUT) is compared against a first constant valueK1. The first constant value K1 is selected to be relatively small,typically about fifty revolutions per minute. If the magnitude of thedifference between the clutch input shaft speed signal V_(IN) and theclutch output shaft speed signal V_(OUT) is greater than the firstconstant value K1, then the clutch 12 is not close to full engagement.Thus, the algorithm 50 branches back to the second step 52, wherein theelectronic controller 20 again determines the engagement rate of theclutch 12 in response to the operating conditions of the vehicle. Thisloop of the algorithm 50 is repeated until the magnitude of thedifference between the clutch input shaft speed signal V_(IN) and theclutch output shaft speed signal V_(OUT) is less than or equal to thefirst constant value K1.

If the magnitude of the difference between the clutch input shaft speedsignal V_(IN) and the clutch output shaft speed signal V_(OUT) is lessthan or equal to the first constant value K1, it can be inferred thatthe clutch 12 is sufficiently close to full engagement as to warrant theinterruption of the gradual engagement process and immediately move therelease bearing 33 from its current position to the fully engagedposition. This interruption is desirable because it decreases theoverall time required to complete the engagement process, whilepreventing the engine from stalling and avoiding undesirable suddenjerking movement of the vehicle. In practice, however, it has been foundthat during the engagement of the clutch 12, the driven disc assembly isnot always frictionally engaged between the flywheel and the pressureplate in a smooth manner. Rather, in some instances, the driven discassembly is frictionally engaged in a somewhat stuttering or hesitatingmanner. If the samplings of the clutch input shaft speed signal V_(IN)and the clutch output shaft speed signal V_(OUT) are made during thisstuttering engagement of the clutch 12, a false inference of fullengagement of the clutch 12 may be generated when, in fact, the clutch12 is not yet sufficiently close to full engagement as to warrant theinterruption of the gradual engagement process.

To address this, the algorithm 50 includes a second decision point 58,wherein the clutch input shaft speed signal V_(IN) is compared with thedesired engine speed signal V_(ENG). Specifically, the magnitude of thedifference between the clutch input shaft speed signal V_(IN) and thedesired engine speed signal V_(ENG) is compared against a secondconstant value K2. Alternatively, the magnitude of the differencebetween the clutch output shaft speed signal V_(OUT) and the desiredengine speed signal V_(ENG) could be compared against the secondconstant value K2. In either event, the second constant value K2 isselected to be relatively small, typically about twenty revolutions perminute. When the magnitude of the difference between the clutch inputshaft speed signal V_(IN) and the desired engine speed signal V_(ENG) isgreater than the second constant value K2, then it can be inferred thatthe clutch 12 is not close to full engagement. Thus, the gradualengagement process is continued, and the algorithm 50 branches back tothe second step 52 as described above. This loop of the algorithm 50 isrepeated until the magnitude of the difference between the clutch inputshaft speed signal V_(IN) and the desired engine speed signal V_(ENG) isless than or equal to the second constant value K2. When the magnitudeof the difference between the clutch input shaft speed signal V_(IN) andthe desired engine speed signal V_(ENG) is less than or equal to thesecond constant value K2, then the inference that the clutch 12 issufficiently close to full engagement is confirmed. Thus, the algorithm50 enters the ninth step 59 wherein the engage valve 41 is actuated tointerrupt the gradual engagement process and immediately move therelease bearing 33 from its current position to the fully engagedposition.

Referring now to FIG. 4, there is illustrated a flow chart of a secondembodiment of an algorithm, indicated generally at 60, for controllingthe movement of the release bearing 33 in its engagement movement fromthe kiss point to the engaged position. In the first step 61 of thealgorithm 60, the electronic controller 20 issues a command to theengine controller 23 setting a desired engine speed signal V_(ENG). Asdiscussed above, the desired engine speed signal V_(ENG) is selected tobe sufficiently high such that the engine 11 is capable of overcomingthe inertia of the vehicle as the clutch 12 is engaged and thereby avoidstalling during the engagement process. The second step 62 of thealgorithm 60 is to determine the engagement rate of the release bearing33 of the clutch 12 and to determine a clutch engagement profile. Asdiscussed above, the engagement rate can be determined in anyconventional manner. The clutch engagement profile represents apreferred rate at which the clutch input shaft speed signal V_(IN) andthe clutch output shaft speed signal V_(OUT) approach synchronization.The clutch engagement profile may, for example, be a curve which isstored within the electronic controller 20 and is used to control theengagement rate of the release bearing 33 in a manner described below.If desired, a plurality of clutch engagement profiles may be storedwithin the electronic controller 20, and a desired one of such curvesmay be selected for use in response to certain operating conditions ofthe vehicle. As shown in the third step 63 of the algorithm 60, theengage valve 41 and the disengage valve 42 are actuated (by means of therespective solenoids 44 and 45) to effect movement of the releasebearing 33 of the clutch 12 according to the selected engagement rate.Thus, the clutch engagement process is initiated.

Next, the fourth step 64 of the algorithm 60 causes the electroniccontroller 20 to read the clutch input shaft speed signal V_(IN) fromthe engine controller 23. In the fifth step 65 of the algorithm 60, theelectronic controller 20 reads the transmission output shaft speedsignal directly from the speed sensor 21. The sixth step 66 in thealgorithm 60 is to calculate the clutch output shaft speed signalV_(OUT). The clutch output shaft speed signal V_(OUT) can be calculatedby multiplying the transmission output shaft speed with the selectedgear ratio of the transmission 13. In the seventh step 67 of thealgorithm 60, a difference signal V_(DIFF) is calculated as thedifference between the clutch input shaft speed signal V_(IN) and theclutch output shaft speed signal V_(OUT). The difference signal V_(DIFF)is stored in the electronic controller 20 for later use.

In the next three steps 68, 69, and 70 of the algorithm 60, theelectronic controller 20 reads an updated clutch input shaft speedsignal V_(IN+1) from the engine controller 23, reads an updatedtransmission output shaft speed signal from the speed sensor 21, andcalculates an updated clutch output shaft speed signal V_(OUT+1). Then,in step 71 of the algorithm 60, an updated difference signal V_(DIFF+1)is calculated as the difference between the updated clutch input shaftspeed signal V_(IN+1) and the updated clutch output shaft speed signalV_(OUT+1). In the next step 72, the algorithm 60 compares the updateddifference signal V_(DIFF+1) with a constant value K. When the magnitudeof the updated difference signal V_(DIFF+1) is less than or equal to theconstant value K, it can be inferred that the clutch 12 is sufficientlyclose to full engagement as to warrant the interruption the gradualengagement process and immediately move the release bearing 33 from itscurrent position to the fully engaged position. Thus, the algorithm 60enters the step 73 wherein the engage valve 41 is actuated to interruptthe gradual engagement process and immediately move the release bearing33 from its current position to the fully engaged position. If desired,the above-discussed secondary step of comparing the magnitude of thedifference between the clutch input shaft speed signal V_(IN) (or clutchoutput shaft speed signal V_(OUT)) and the desired engine speed signalV_(ENG) against the second constant value K2 may be performed as well.

When the magnitude of the updated difference signal V_(DIFF+1) isgreater than the constant value K, it can be inferred that the clutch 12is not yet sufficiently close to full engagement as to warrant theinterruption the gradual engagement process and immediately move therelease bearing 33 from its current position to the fully engagedposition. Thus, the algorithm 60 next enters a step 74 wherein an errorsignal V_(ERR) is calculated as the difference between the updateddifference signal V_(DIFF+1) and the prior difference signal V_(DIFF).This error signal V_(ERR) is next compared in step 75 with thepreviously determined clutch engaged profile. If the error signalV_(ERR) corresponds closely to the clutch engagement profile, then theengagement process continues. However, if the error signal V_(ERR)deviates from the clutch engagement profile by more than a predeterminedamount, then the modulation of the engage valve 41 is adjusted such thatthe movement of the release bearing 33 of the clutch 12 more closelyfollows the clutch engagement profile, as shown in step 76. Thus, theelectronic controller 20 controls the movement of the release bearing 33of the clutch 12 to closely follow the selected clutch engagementprofile so as to consistently engage the clutch 12.

The last step in the algorithm 60 is, as shown in step 77, to re-definethe prior difference signal V_(DIFF) as the updated difference signalV_(DIFF+1). Then the algorithm 60 loops back to step 68 wherein theupdated clutch input shaft speed signal V_(IN+1) is read, the updatedclutch output shaft speed V_(OUT+1) is calculated, and the updateddifference signal V_(DIFF+1) is calculated. Thus, the algorithm 60continuously monitors the updated clutch input shaft speed signalV_(IN+1) with the constant K to determine when to complete the shiftingprocess and, when that does not occur, continuously controls themovement of the release bearing 33 of the clutch 12 to closely followthe selected clutch engagement profile so as to consistently engage theclutch 12.

In accordance with the provisions of the patent statutes, the principleand mode of operation of this invention have been explained andillustrated in its preferred embodiment. However, it must be understoodthat this invention may be practiced otherwise than as specificallyexplained and illustrated without departing from its spirit or scope.

What is claimed is:
 1. An apparatus for controlling an engagement rateof a clutch having an input member and an output member for selectivelyconnecting an engine to a transmission, the apparatus comprising: afirst sensor for generating a signal that is representative of therotational speed of the input member of the clutch; a second sensor forgenerating a signal that is representative of the rotational speed ofthe output member of the clutch; a controller for generating a desiredengine speed signal and a control signal that is representative of anengagement rate of the clutch, said controller being responsive to saidfirst sensor signal, said second sensor signal, and said desired enginespeed signal for modifying said control signal to increase theengagement rate of the clutch when (1) the rotational speeds of theinput member of the clutch and the output member of the clutch differ byless than a predetermined amount, and (2) the rotational speed of theinput member of the clutch and the desired engine speed differ by lessthan a predetermined amount; and a clutch actuator for controlling theengagement rate of the clutch in response to said control signal.
 2. Theapparatus defined in claim 1 wherein the rotational speeds of the inputmember of the clutch and the output member of the clutch differ by lessthan a first predetermined amount, and wherein the rotational speed ofthe input member of the clutch and the desired engine speed differ byless than a second predetermined amount different from said firstpredetermined amount.
 3. The apparatus defined in claim 2 wherein saidfirst predetermined amount is about fifty revolutions per minute.
 4. Theapparatus defined in claim 2 wherein said second predetermined amount isabout twenty revolutions per minute.
 5. The apparatus defined in claim 1wherein the output member of the clutch is an input member to thetransmission, the transmission further includes an output member, saidsecond sensor generates a signal that is representative of therotational speed of the output member of the transmission, and saidcontroller is responsive to said signal from said second sensor forcalculating the rotational speed of the output member of the clutch. 6.An apparatus for controlling an engagement rate of a clutch having aninput member and an output member for selectively connecting an engineto a transmission, the apparatus comprising: a first sensor forgenerating a signal that is representative of the rotational speed ofthe input member of the clutch; a second sensor for generating a signalthat is representative of the rotational speed of the output member ofthe clutch; a controller for generating a desired engine speed signaland a control signal that is representative of an engagement rate of theclutch, said controller being responsive to said first sensor signal andsaid second sensor signal for modifying said control signal to increasethe engagement rate of the clutch when the rotational speeds of theinput member of the clutch and the output member of the clutch differ byless than a predetermined amount, said controller being furtherresponsive to said first sensor signal and said second sensor signal fordetermining the magnitude of the difference therebetween and formodifying said control signal in response to said magnitude of saiddifference; and a clutch actuator for controlling the engagement rate ofthe clutch in response to said control signal.
 7. The apparatus definedin claim 6 wherein said predetermined amount is about fifty revolutionsper minute.
 8. The apparatus defined in claim 6 wherein the outputmember of the clutch is an input member to the transmission, thetransmission further includes an output member, said second sensorgenerates a signal that is representative of the rotational speed of theoutput member of the transmission, and said controller is responsive tosaid signal from said second sensor for calculating the rotational speedof the output member of the clutch.